In general, this invention relates to apparatus and methods for testing flexible containers traveling at high speed on a production line. More specifically, the invention relates to apparatus and methods for testing the internal pressure, fluid tightness and/or seal integrity of containers by indirect contact and especially, but not exclusively, is intended for use in testing flexible walled containers made of plastic and/or thin-walled metals.
In many industries, it is important to test for internal pressure, fluid tightness and/or seal integrity. In the beverage industry, for example, it is essential to assure that containers in which beverage products reside are completely sealed to assure that their contents are in good condition, free from molds, bacteria and other pathogenic organisms so that they will be safe when used by consumers. The pharmaceutical industry similarly requires that containers for medications, especially solutions intended for injection or intravenous administration, be protected from contamination or serious danger to public health may result. Similar considerations apply to the food industry, as well, where food products are delivered in sealed, flexible-walled containers.
In the beverage industry, it is also common practice to place metered doses of carbon dioxide or liquid nitrogen in containers immediately prior to or contemporaneous with their sealing to increase their internal pressure as an means of enhancing their stiffness, thereby reducing material costs while still providing filled containers possessing acceptably robust structural integrity so that they can withstand the rigors of handling, packing, and shipment.
Because fluid tightness and seal integrity of containers is not readily ascertained by visual inspection, various attempts have been made to provide apparatus for testing for these properties. For example, U.S. Pat. No. 4,862,732 describes a “squeezing apparatus” for testing the fluid tightness and/or seal integrity of plastic bottles, such as those in which laundry detergents are commonly sold. This apparatus creates a pressure within the bottle by squeezing it by means of a pneumatic cylinder. It monitors the position of the piston of this cylinder. If the bottle does not leak, the piston stops as soon as the pressure in the bottle increases enough to balance the force of the piston. After equilibrium, continued pressure caused by the squeezing diminishes as pressurized gas within the bottle leaks by being forced through a leak hole, and thus the piston of the pneumatic cylinder moves further than in the case of a non-leaking bottle.
U.S. Pat. No. 5,767,392 to William David Belcher, et al. issued on Jun. 16, 1998 describes a method and apparatus for leak testing a closed container by applying a compressive force to the container, releasing the compressive force, and measuring the recovery of the container a predetermined time after the compressive force is released. The recovery is correlated with the presence or absence of leaks. The Belcher, et al. patent appears to suffer from the inability to cope with variations in container temperature and physical properties of the container and its contents.
U.S. Pat. No. 4,800,932 to Masayuki Masuda, et al. issued on Jan. 31, 1989 describes an apparatus for determining internal pressure of a filled can by measuring the reaction force from the can as it is passed between back up and measurement rollers, at least one of which is crowned.
U.S. Pat. No. 6,427,524 issued to Frank Raspante, et al. on Aug. 6, 2002 describes apparatus and methods for in-line testing for leaks in flexible containers traveling along a production line at high speeds through the use of multiple sensors spaced at fixed displacements along a compression section.
In spite of the variety of approaches in the art, there remains a need to be able to measure containers without inflicting structural or aesthetic damage to them as a result of the measurement process, and it is a primary object of this invention to satisfy that need.
It is another object of the present invention to provide high-speed apparatus and methods for assessing the internal pressure of containers without removing them from a production line.
It is another object of the present invention to provide apparatus and methods for in-line leak testing of flexible containers while automatically compensating for container to container variations in temperature and physical properties.
It is another object of the present invention to provide in-line apparatus and methods for testing containers for seal integrity.
It is yet another object of the present invention to provide apparatus and methods for in-line testing of containers while generating statistical data for process control and quality assurance purposes.
It is yet another object of the present invention to provide apparatus and methods for in-line testing of containers to provide feedback signals for control of upstream production apparatus.
Other objects of the invention will, in part, be obvious and will, in part, appear hereinafter when the description to follow is read in conjunction with the drawings.